linux-kernel - Re: [PATCH AUTOSEL 5.8 28/29] spi: fsl-dspi: fix use-after-free in remove path

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Date:   Tue, 29 Sep 2020 08:22:16 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Mark Brown <broonie@...nel.org>, linux-spi@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.8 28/29] spi: fsl-dspi: fix use-after-free in
 remove path

Hi Sasha,

On Mon, Sep 28, 2020 at 09:30:25PM -0400, Sasha Levin wrote:
> From: Sascha Hauer <s.hauer@...gutronix.de>
> 
> [ Upstream commit 530b5affc675ade5db4a03f04ed7cd66806c8a1a ]
> 
> spi_unregister_controller() not only unregisters the controller, but
> also frees the controller. This will free the driver data with it, so
> we must not access it later dspi_remove().
> 
> Solve this by allocating the driver data separately from the SPI
> controller.
> 
> Signed-off-by: Sascha Hauer <s.hauer@...gutronix.de>
> Link: https://lore.kernel.org/r/20200923131026.20707-1-s.hauer@pengutronix.de
> Signed-off-by: Mark Brown <broonie@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  drivers/spi/spi-fsl-dspi.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)

This patch causes a regression and shouldn't be applied without the fix
in https://lkml.org/lkml/2020/9/28/300.

Sascha

> index 91c6affe139c9..aae9f9a7aea6c 100644
> --- a/drivers/spi/spi-fsl-dspi.c
> +++ b/drivers/spi/spi-fsl-dspi.c
> @@ -1273,11 +1273,14 @@ static int dspi_probe(struct platform_device *pdev)
>  	void __iomem *base;
>  	bool big_endian;
>  
> -	ctlr = spi_alloc_master(&pdev->dev, sizeof(struct fsl_dspi));
> +	dspi = devm_kzalloc(&pdev->dev, sizeof(*dspi), GFP_KERNEL);
> +	if (!dspi)
> +		return -ENOMEM;
> +
> +	ctlr = spi_alloc_master(&pdev->dev, 0);
>  	if (!ctlr)
>  		return -ENOMEM;
>  
> -	dspi = spi_controller_get_devdata(ctlr);
>  	dspi->pdev = pdev;
>  	dspi->ctlr = ctlr;
>  
> @@ -1414,7 +1417,7 @@ static int dspi_probe(struct platform_device *pdev)
>  	if (dspi->devtype_data->trans_mode != DSPI_DMA_MODE)
>  		ctlr->ptp_sts_supported = true;
>  
> -	platform_set_drvdata(pdev, ctlr);
> +	platform_set_drvdata(pdev, dspi);
>  
>  	ret = spi_register_controller(ctlr);
>  	if (ret != 0) {
> @@ -1437,8 +1440,7 @@ static int dspi_probe(struct platform_device *pdev)
>  
>  static int dspi_remove(struct platform_device *pdev)
>  {
> -	struct spi_controller *ctlr = platform_get_drvdata(pdev);
> -	struct fsl_dspi *dspi = spi_controller_get_devdata(ctlr);
> +	struct fsl_dspi *dspi = platform_get_drvdata(pdev);
>  
>  	/* Disconnect from the SPI framework */
>  	spi_unregister_controller(dspi->ctlr);
> -- 
> 2.25.1
> 
> 

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